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cachefiles: fix the race between cachefiles_bury_object() and rmdir(2)
the victim might've been rmdir'ed just before the lock_rename();
unlike the normal callers, we do not look the source up after the
parents are locked - we know it beforehand and just recheck that it's
still the child of what used to be its parent. Unfortunately,
the check is too weak - we don't spot a dead directory since its
->d_parent is unchanged, dentry is positive, etc. So we sail all
the way to ->rename(), with hosting filesystems _not_ expecting
to be asked renaming an rmdir'ed subdirectory.
The fix is easy, fortunately - the lock on parent is sufficient for
making IS_DEADDIR() on child safe.
Cc: stable@vger.kernel.org
Fixes: 9ae326a690
(CacheFiles: A cache that backs onto a mounted filesystem)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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@ -343,7 +343,7 @@ try_again:
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trap = lock_rename(cache->graveyard, dir);
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trap = lock_rename(cache->graveyard, dir);
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/* do some checks before getting the grave dentry */
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/* do some checks before getting the grave dentry */
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if (rep->d_parent != dir) {
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if (rep->d_parent != dir || IS_DEADDIR(d_inode(rep))) {
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/* the entry was probably culled when we dropped the parent dir
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/* the entry was probably culled when we dropped the parent dir
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* lock */
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* lock */
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unlock_rename(cache->graveyard, dir);
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unlock_rename(cache->graveyard, dir);
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